Apparatus for cutting a slot in a foundation mass for determining deformability and residual stresses in the foundation mass

ABSTRACT

Apparatus for cutting a narrow slot in a foundation mass for measuring the deformability and the residual stress in the mass, the slot being formed by cutting a plurality of contiguous narrow slots with a rotatable cutting disc to a depth greater than the radius of the disc, whereafter a flat jack is inserted into the elongated slot and applies measured pressure against the faces bounding the slot whereby the faces undergo deformation which is measured by the jack.

United States Patent da Rocha et a1.

[54] APPARATUS FOR CUTTING A SLOT IN A FOUNDATION MASS FOR DETERMININGDEFORMABILITY AND RESIDUAL STRESSES IN THE FOUNDATION MASS [72]Inventors: Manuel Coelho Mendes da Rocha,

Av. Estados Unidos da America, 95- 3D.; Jorge Neves da Silva, Rua CaboVerde 14-2D., both of Lisbon, Portugal [22] Filed: June 12, 1970 [21]Appl. No.: 45,772

Related US. Application Data [62] Division of Ser. No. 731,673, May 6,1968, Pat.

[52] US. Cl. ..299/38, 299/78, 175/173, 125/14, 125/19 [51] Int. Cl...E2lc 25/06, E2lc 39/00 [58] Field of Search ..299/39, 40, 50, 36, 37;

[451 Sept. 19, 1972 [56] References Cited UNITED STATES PATENTS2,247,215 6/1941 Wegner et a] ..125/19 X 3,323,507 6/ 1 967 Schuman 125/14 3,533,283 10/1970 da Rocha et al ..73/94 3,325,946 6/1967 Lange..51/33 R Primary Examiner-Richard C. Queisser AssistantExaminer--Marvin Smollar Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT Apparatus for cutting a narrow slot in a foundation mass formeasuring the deformability and the residual stress in the mass, theslot being formed by cutting a plurality of contiguous narrow slots witha rotatable cutting disc to a depth greater than the radius of the disc,whereafter a flat jack is inserted into the elongated slot and appliesmeasured pressure against the faces bounding the slot whereby the facesundergo deformation which is measured by the jack.

3 Claims, 5 Drawing Figures v PATENTEI'JSEPIQ m2 3.692.357

SHEET 3 [IF 4 APPARATUS FOR CUTTING A SLOT IN A FOUNDATION MASS FORDETERMINING DEFORMABILITY AND RESIDUAL STRESSES IN THE FOUNDATION MASSCROSS RELATED APPLICATION This application is a divisional applicationof my earlier application Ser. No. 731,673, filed May 6, I968, now U.S.Pat. No. 3,533,283.

BRIEF SUMMARY OF THE INVENTION:

This invention relates to apparatus for cutting slots in a foundationmass for the purpose of measuring the deformability and residualstresses in the foundation mass.

It is increasingly recognized as very important to know thedeformability of foundation masses such as soils, rock masses, and thelike when designing large structures to be built on or within rockmasses, such as concrete dams, bridges, large buildings, tunnels,underground power stations, etc.

Very often the deformability of these foundations is determinedexclusively in laboratory tests of soil or rock samples. Recently,however, the need for in situ tests have been recognized, at least inthe case of large structures involving large volumes of foundationrocks, so as to secure representative results of the true conditions inthe ground, particularly as regards heterogeneity and cracks.

These in situ tests generally comprise excavating trenches or galleries,applying known forces on given areas of their walls and measuring theresulting displacements.

These forces are applied by means of rigid concrete slabs cast againstthe gallery wall, with which they are in contact in an area of theorder, for example, of 1 square meter. By means of jacks applied to theslab, it is possible to obtain pressures representative of those thatwill be applied to the ground by the completed structure. Circular steelplates with diameters of 20 or 50 cm can be used for the same purpose.

Nevertheless, the distribution in the ground of the forces transmittedby concrete slabs or steel plates is imperfectly known, and makes theinterpretation of the test results difficult. In order to surmount thisdifficulty, it is sought to obtain a distribution as uniform as possibleof the loads in the ground, for which rubber plates are sometimes usedbetween the loaded surface and the jacks.

A still more uniform distribution of pressure can be obtained by meansof oil-filled deformable flat jacks. These jacks are applied in narrowslots cut in the rock mass and usually cannot be reused because thespace between the jack and the slot is filled with mortar or concrete.

In deformability tests, strains are measured in the direction of theapplied forces sometimes at the center of, sometimes outside, the loadedareas.

From the above, it follows that the methods so far used in deformabilitytests of soils and rocks are very expensive and slow, due to the need todrive a gallery or cut a slot in the rock mass to be studied. Blastingmethods have the disadvantage of disturbing the structure of the soil orrock mass, possibly changing the values to be determined, however greatthe precautions taken.

Additionally, the volume of ground involved in the tests by the methodsnow in use is not as a rule sufficiently large to be representative ofthe properties of the whole. In practice, tests in which the loaded areaexceeds 1 square meter are too slow, and the are of loading is generallynot more than 0.25 square meters,

and, save in special cases, such an area is obviously insufficient.

An object of the invention is to avoid the disadvantages indicatedhereinabove and to provide novel apparatus for cutting the slot in thefoundation mass and a new instrument by which soil deformability can bedetermined under the following conditions:

the surfaces to be tested can be exposed by comparatively rapid andinexpensive methods;

test surfaces can be obtained which are entirely smooth, very extensiveand reaching to a considerable depth in the rock mass;

the flat jacks which apply the pressure contain strainmeasuringinstruments and can be easily reused; the rock mass is not disturbedwhen the slot is cut.

In accordance with the present invention narrow slots are successivelycut by means of a disc with a diameter of, for example, 1 m.

A slight overlap in the contiguous ends of successive slots makes itpossible to obtain a single slot with approximately the same length asthe sum of individual slots.

The depth of the slots can exceed the radius of the cutting disc, as acylindrical hole of suitable diameter is previously bored to accommodatea tubular support of the disc. This support, which acts as a guide forthe cutting operation, can be extended by means of similar units so thatslots can be cut to any depth.

In order to obtain a continuous surface for applying uniform pressureson the walls of the slot, these are extended by means of twocomparatively rigid semi-cylinders with adequate dimensions which areintroduced in the guide hole. It is only after this operation iscompleted that a flat jack containing strain measuring instruments andthe fluid under pressure in introduced in the slot to displace the wallsof the slot.

From the values of the two parameters, pressure and displacement of theslot faces, it is possible by means of analytic or empirical formulas toobtain the modulus of deformability of the foundation mass.

If the distances between points, for instance at the surface, aremeasured before cutting the slot, the residual stress in the groundnormal to the plane of the flat jack is equal to the pressure requiredto cancel the change in the distance between the points observed duringthe cutting of the slot.

BRIEF DESCRIPTION OF THE DRAWING:

FIG. 1 is a side view, partly broken away and in sections, of a cuttinginstrument;

FIG. 2 is a front view of the cutting instrument;

FIG. 3 is a side view of a flat jack with a shape suitable to completelyfill a slot which is cut in the material to be measured;

FIG. 4 is a side view of a flat jack with a different shape to be usedwhen the slot is not to be entirely filled; and

FIG. 5 is a sectional view showing the location of a strain measuringinstrument in the jack.

DETAILED DESCRIPTION:

The cutting apparatus comprises a supporting frame having a base 1bolted in the ground, two guiding columns 2 connected by an uppertransverse element, and two braces 3 between he transverse element andthe base to increase the rigidity of the assembly.

Each of the two guiding columns 2 is formed with a rack 4 on a flat rearface. The rack 4 extends the entire length of the columns. A carrier 6can be moved vertically up and down along the guiding columns byoperation of a crank 5 which controls two pinions '(now shown) whichengage racks 4.

Carrier 6 contains a gear box 7 operated by a motor 8. This can be anelectric, compressed air, or any other type of motor, although thehydraulic type is preferred due to its compact construction.

A cutting disc 9 is fitted on a shaft 10 which is mounted at the lowerend of a supporting tube 11. The shaft 10 and the disc 9 thereon, isdriven in rotation from the motor 8 through the gear box 7 and a doublechain 23 or other suitable power transfer means contained within tube11. i

A slot is progressively cut in the foundation mass to be tested by thedisc 9 which is advanced by the hand operated crank 5. Before cuttingthe rock with the disc, a guide hole is drilled in the rock with asufficiently large diameter to permit subsequent guided passage of tube11 when the slot is cut by the disc..The bit for drilling the guide holemay be attached to the frame and operated by the same motor 8.

By means of a crank 12 and an eccentric 13, a bracket 24 connected tothe tube 11 can be given a lateral oscillatory movement to provide' arectilinear or a pendulous movement of tube 11 and disc 9 with respectto carrier 6 and the supporting frame. This facilitates the penetrationof the disc in the rock mass, producing a slight enlargement in thelength of the slot when the slot is being cut.

The tubular support of the disc 11 can be extended by means of similarelements fitted with suitable transmission system so that its length isadapted to correspond with the desired depth of the slot.

After successive slots have been cut to form an elongated slot ofdesired length, a jack is inserted into the slot to apply a measuredpressure on the walls bounding the slot in order to measure thecorresponding deflection of the walls whereby the deformability of thefoundation mass can be measured.

The jacks by which uniform pressure is applied to the slot walls areessentially constituted of two flatted mildsteel flexible sheets 14welded along their edges to define an interior space. Any other highstrength very deformable material can be used instead of mild steel.

Flat jacks intended to fill the entire area of the slot have the shapeof a rectangle with a semi-circular end (FIG. 3). It the flat jacks neednot fill the entire area, they can be smaller and have other shapes,such as that shown in FIG. 4. The latter are used when the edges of theslots are not to be disturbed by applied forces.

Flat jacks of the former type include a flap 15 on the upper edge whichprotects the operators against projections of fluid under pressure incase of a pupture in the jack.

Both types of jacks are fitted with a nipple 15 for the inlet of fluidunder pressure and an outlet 17 for elec tric cables of the strainmeasuring instruments- Each strain measuring instrument IS applied atsuitable points between the faces of the flat jack, as shown in FIG. 5,and consists of two deformable steel blades 18 each fixedly secured atits opposite ends to a respective plate. Electrical resistance straingauges 19 are secured on the blades 18 and are incorporated in aWheatstone bridge circuit and connected with an external readinginstrument, where changes in the distance between the faces of the flatjack can be directly read.

It should be noted that the disclosed apparatus may be modified withoutdeparting from the scope and spirit of the invention as defined in theapended claims.

What is claimed is:

1. Apparatus for cutting a narrow slot in a foundation mass, saidapparatus comprising a frame adapted for placement on a foundation mass,upright columns on said frame, a carrier supported on said frame for upand down movement along said columns, a hollow member having upper andlower ends, said upper end being connected to said carrier for up anddown movement therewith, a thin cutting disc rotably mounted at thelower end of the hollow member to cut a slot in the foundation mass,means for driving the cutting disc in rotation including a prime movermounted on said carrier and means drivingly coupling said prime moverand cutting disc and extending in said hollow member, and means engagingsaid hollow member to apply lateral oscillatory movement thereto as thecutting disc is cutting a slot.

2. Apparatus as claimed in claim 1, comprising manually controlled meanson said carrier for raising and lowering the same on said frame.

3. Apparatus as claimed in claim 2, wherein said manually controlledmeans comprises a crank.

- UNITEDYVSTATESQPAIENT ,QF ICE "CERTIFICATE OF C(JRRECTI-ON Pateflt3,692,357 ..",n' pt m 'l- 1972 i I v I It 15 certified that errorappears the above-identified vpatent and that said Letters Patent arehereby corrected as shown below:

On the cover sheet-,-inser't' [SOI-iF rei-gn Application Priority DataMay 6, 19-67 Portugal .47655 Signed and sealed this, 2nd dayIof'Januairy 1973.

(SEAL) ATTEST:

EDWARD M.FLETCHER,JR. Y ROBERT GOTTSCHALK} Attesting OfficerCommissioner of Patents F ORM PO-] 050 (10-69) USCOMM-DC 60878-1 69 flU,S GQVERNMENT PRINTING OFFICE I969 0-388-33.

1. Apparatus for cutting a narrow slot in a foundation mass, saidapparatus comprising a frame adapted for placement on a foundation mass,upright columns on said frame, a carrier supported on said frame for upand down movement along said columns, a hollow member having upper andlower ends, said upper end being connected to said carrier for up anddown movement therewith, a thin cutting disc rotably mounted at thelower end of the hollow member to cut a slot in the foundation mass,means for driving the cutting disc in rotation including a prime movermounted on said carrier and means drivingly coupling said prime moverand cutting disc and extending in said hollow member, and means engagingsaid hollow member to apply lateral oscillatory movement thereto as thecutting disc is cutting a slot.
 2. Apparatus as claimed in claim 1,comprising manually controlled means on said carrier for raising andlowering the same on said frame.
 3. Apparatus as claimed in claim 2,wherein said manually controlled means comprises a crank.